U.S. patent number 6,682,630 [Application Number 10/088,512] was granted by the patent office on 2004-01-27 for uniform gas distribution in large area plasma source.
This patent grant is currently assigned to European Community (EC). Invention is credited to Pascal Colpo, Fran.cedilla.ois Rossi.
United States Patent |
6,682,630 |
Colpo , et al. |
January 27, 2004 |
Uniform gas distribution in large area plasma source
Abstract
An apparatus configured to generate a time-varying magnetic
field through a field admission window of a plasma processing
chamber to create or sustain a plasma within the chamber by
inductive coupling. The apparatus includes a magnetic core
presenting a pole face structure,--an inductor means associated
with the magnetic core, arranged to generate a time-varying
magnetic field through the pole face structure, and--a device for
injecting gas into the chamber and through the chamber and through
the magnetic core.
Inventors: |
Colpo; Pascal (Annecy,
FR), Rossi; Fran.cedilla.ois (Andronno,
IT) |
Assignee: |
European Community (EC)
(LU)
|
Family
ID: |
8242127 |
Appl.
No.: |
10/088,512 |
Filed: |
March 29, 2002 |
PCT
Filed: |
September 18, 2000 |
PCT No.: |
PCT/EP00/09996 |
PCT
Pub. No.: |
WO01/24220 |
PCT
Pub. Date: |
April 05, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Sep 29, 1999 [EP] |
|
|
99402374 |
|
Current U.S.
Class: |
156/345.48;
118/715; 118/723I; 156/345.33; 156/345.49 |
Current CPC
Class: |
H01J
37/321 (20130101); H01J 37/3244 (20130101) |
Current International
Class: |
H01J
37/32 (20060101); C23C 016/00 (); H01L
021/00 () |
Field of
Search: |
;118/723I,723IR,723AN,715,723R,723E,723MR,723MA
;156/345.48,345.49,345.47,345.33,345.34,345.42,345.46
;204/298.07,298.16,298.33,298.37 ;315/111.51 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Alejandro-Mulero; Luz
Attorney, Agent or Firm: Bacon & Thomas, PLLC
Claims
What is claimed is:
1. An apparatus for generating a time-varying, magnetic field in a
plasma processing chamber (20) to create or sustain a plasma within
the chamber by inductive coupling, comprising: a magnetic core (38;
138) presenting a pole face (38a; 39a) an inductor (40) associated
with the magnetic core arranged to generate a time-varying magnetic
field throughout the pole face, injector apparatus
(42,43,44,45,48,49,51,91,93,95,142,144) arranged to inject gas into
said chamber (20) and through said magnetic core.
2. The apparatus according to claim 1, wherein said injector
apparatus forms a showerhead-like gas injection (52, 54).
3. The apparatus according to claim 1 wherein said injector
apparatus comprises a plurality of injection pipes (42, 43, 44,
45,142, 144) distributed or disposed through the magnetic core.
4. The apparatus according to claim 3, wherein said pipes are
connected to gas distributing apparatus (48, 48a, 48b, 49, 51, 91,
93, 95) arranged to distribute gas to the injection pipes.
5. The apparatus according to claim 4, said gas distributing
apparatus being located on the side of the magnetic core opposite
to an inner space (50) of said plasma processing chamber (20).
6. The apparatus according to claim 4, said gas distributing
apparatus comprising a common gas distributing pipe (48, 48a, 48b,
49), through which gas is distributed to the injection pipes.
7. The apparatus according to claim 4, said gas distributing
apparatus comprising a cover (91), located on the side of the
magnetic core opposite to an inner space (50) of said plasma
processing chamber (20), with a gap (93) between said cover and
said magnetic core, said injection pipes (42, 44) being open in
said gap.
8. The apparatus according to claim 3, said injection pipes being
made of a material selected from the group consisting of stainless
steel and an insulating material.
9. The apparatus according to claim 3, said injection pipes having
different diameters from each other.
10. A plasma processing apparatus comprising: a plasma processing
chamber (20) having at least one field admission window (122, 122a,
122b), at least one magnetic field generating apparatus according
to claim 3, arranged to create a time-varying magnetic field in the
chamber by inductive coupling through a corresponding field
admission window, each of said injection pipes traversing said
window through a corresponding hole in said window, and an end of
each of said injection pipes being welded to the periphery of said
corresponding hole, a power source (60) arranged to drive the
magnetic field generating apparatus.
11. The apparatus according to claim 10, further comprising a
workpiece support (38, 40; 142) adapted to hold at least one
workpiece (26) at portions outside surfaces of the workpiece(s) to
be exposed to an energy field from the two or more field admission
windows (122a, 122b).
12. The apparatus according to claim 11, wherein the workpiece
support (38, 40; 142) is adapted to hold at least one workpiece
(26) at edge portions thereof.
13. The apparatus according to claim 1, said pole face (38a) being
curved.
14. The apparatus according to claim 1, wherein the pole face (38)
is constituted by a single pole face (38a) of unitary
construction.
15. The apparatus according to claim 1, wherein the pole face (38)
is divided into two or more pole faces that confront respective
portions of the plasma processing chamber.
16. The apparatus according to claim 15, wherein the divided pole
faces are associated to respective inductors and power supplies
whilst being kept in phase to ensure that all the pole faces have
the same polarity at any one time.
17. The apparatus according to claim 15, wherein the divided pole
faces physically depend from a common magnetic core and
inductor.
18. The apparatus according to claim 1, wherein the pole face (38a)
constitutes an end face of the magnetic core (38).
19. The apparatus according to claim 1, wherein the magnetic core
comprises at least one discontinuity (37) so as to prevent the
circulation of eddy currents around the core.
20. The apparatus according to claim 19, wherein the discontinuity
is in the form of one or more laminations (37).
21. The apparatus according to claim 20, wherein the lamination(s)
(37) extend(s) radially from a point proximal to or at the centre
of the core (38) to the periphery of the core.
22. The apparatus according to claim 1, wherein said core (38) has
a unitary structure.
23. The apparatus according to claim 1, wherein the inductor (40)
comprises a conductor arranged to form one or more turns around at
least a portion of the magnetic core (38).
24. The apparatus according to claim 1, wherein the inductor (40)
is wound around the periphery of the magnetic core (38).
25. The apparatus according to claim 1, wherein the inductor (40)
comprises a planar winding recessed within a groove (47) or groove
pattern (46) formed in the magnetic core, on the pole face (38a;
39a).
26. The apparatus according to claim 1, wherein the inductor (40)
is driven by a power supply (61) delivering power at a frequency of
around 10 kHz to 100 MHz, preferably at a frequency of 13.56
MHz.
27. The apparatus according to claim 1, further comprising biasing
apparatus arranged to bias the core with at least one bias selected
from the group consisting of: an ac bias (including radio
frequencies), a dc bias, and a ground bias.
28. The apparatus according to claim 1, further comprising cooling
apparatus arranged to cool the core (26).
29. A plasma processing apparatus comprising: a plasma processing
chamber (20) having at least one field admission opening (94a,
94b), at least one magnetic field generating apparatus according to
claim 1, arranged to create a time-varying magnetic field in the
chamber, a power source arranged to drive the magnetic field
generating apparatus.
30. The apparatus according to claim 29, further comprising a
barrier (80, 80a; 80b) formed between a field emission surface and
the plasma environment arranged so as to prevent that surface from
contaminating the chamber (20).
31. The apparatus according to claim 30, said barrier comprising a
sheet of dielectric material (80, 80a, 80b) maintained between said
pole face structure and an inner space of said plasma processing
chamber(20).
32. The apparatus according to claim 31, a distance between said
sheet of dielectric material and said face structure being less
than 1 mm.
33. The apparatus according to claim 30, wherein the barrier (80)
is mounted without contacting a field emission face of the magnetic
field generating apparatus, the barrier being held at one of the
periphery of the field emission face and the process chamber
(20).
34. The apparatus according to claim 33 wherein a pressure adjuster
is provided to balance the pressure conditions between the inner
and outer faces of the barrier (80).
35. The apparatus according to claim 34, wherein the pressure
adjuster comprises a valve arrangement arranged and operative to
allow the pressure at the outer face of the barrier (80) to follow
that of the process chamber (20) when the latter is submitted to
changing pressure conditions, for example, during vacuum pumping or
gas admission, or setting to atmospheric pressure for loading and
unloading a workpiece, and to seal off the space above the outer
surface of surface of the barrier when the chamber is operative for
plasma processing such that no contaminant from the energy field
generator can reach the plasma environment of the process
chamber.
36. The Apparatus according to claim 29, said magnetic core or said
pole face having an active field emission area whose size and shape
matches or substantially matches the field admission opening or the
field admission window.
37. The apparatus according to claim 29, one of said magnetic core
and said pole face having an active field emission area whose size
and shape is smaller than an area of the field admission opening or
the field admission window.
38. The apparatus according to claim 29, further comprising at
least one field admission window (122) between an inner space (50)
of said plasma chamber and said magnetic field generating
apparatus.
39. The apparatus according to claim 38, said magnetic core
presenting a face being adapted to be applied against or in
proximity to the window (122).
40. The apparatus according to claim 38, said inductive type plasma
processing chamber (20) having two or more windows (122a, 122b) for
receiving induced field energy, each window enabling induced field
energy to enter the chamber from a respective direction.
41. The apparatus according to claim 40, provided with at least one
pair of oppositely-facing windows (122a, 122b).
42. The apparatus according to claim 38, further comprising one or
more partitions to isolate spaces therein associated with one or a
group of windows (122a, 122b).
43. The apparatus according to claim 38, wherein the windows (122a,
122b) are non planar to follow a contour of a wall portion from
which they depend.
44. A plasma processing apparatus comprising: a plasma processing
chamber (20) having at least one field admission window (122), at
least one magnetic field generating apparatus according to claim 1,
arranged to create a time-varying magnetic field in the chamber by
inductive coupling through a corresponding field admission window,
said injector apparatus and through said magnetic core traversing
said window, a power source (61) arranged to drive the magnetic
field generating apparatus.
45. Use of a plasma processing chamber according to claim 1 for
processing a workpiece (16).
Description
TECHNICAL FIELD AND RELATED ART
The present invention relates generally to apparatus and their use
for surface treatments using plasma assisted processing and more
particularly, but not exclusively, for the treatment of large flat
substrates.
Such treatments can include etching, deposition, cleaning,
passivation and ion implantation.
The new requirements for the plasma processing of large substrates
become more and more critical for plasma sources available on the
market. The success of the plasma assisted processing depends on
the scalability of these plasma sources.
To fulfill these requirements, new plasma sources must be envisaged
to process large substrates with plasma features like the
generation of high densities of reactive species with low and
controllable energy over a wide pressure range, and with an
excellent homogeneity throughout the substrate.
Plasma processing generally uses a vacuum chamber connected to a
gas inlet and a pumping device for controlling the gas flows and
pressure. Electrical energy is applied to the vacuum chamber to
accelerate the free electrons in the gases to the energy of
ionization of the gas molecules, which thereby creates plasma.
Ionization phenomena free some electrons which can also be
accelerated to the ionization energy.
The added energy of the free electrons in the gas is generally
accomplished by an electric field, a varying magnetic field, or
both.
One traditional method used in plasma processing to generate plasma
is by a technique known as Capacitively Coupled Plasma. The plasma
results from the application of an AC voltage between two
electrodes creating an electric field which accelerate the free
electrons. Generally, one of the two electrodes is the substrate
holder. The applied energy generated by the AC voltage applied
between the two electrodes controls at the same time the flux and
kinetic energy of the ions. Because the two parameters are coupled,
this process is difficult to optimize.
Another plasma source used in plasma processing is based on the
Electron Cyclotron Resonance (ECR). In this process, microwave
power is applied to the gas together with a constant magnetic field
which transforms the electron paths into a circular path. The
intensity of the magnetic field is such that the frequency of
gyration of the electron is the same as the frequency of the
electric field, which leads to a resonance effect increasing the
efficiency of electron acceleration. This type of excitation mode
can provide a plasma with high ion flux and low ion energy. The ion
energy can be controlled by applying an independent bias to the
substrate. However, such an apparatus is complex and expensive.
Moreover, it is still too limited as regards the plasma expected
processing expected features, in particular for scaling up and
homogeneity of the plasma source.
A new generation of plasma source has been developed during the
last years which give good promise. These are known as Inductively
Coupled Plasmas (ICPs), such as described e.g. in U.S. Pat. Nos.
4,948,458 and 5,277,751. The plasma is created by a varying
magnetic field generated by a spiral planar coil. The electrons are
accelerated in a circular path parallel to the coil plane and the
insulating window of the plasma chamber. This configuration
provides a high density plasma with low kinetic energy, but has an
inherent problem of homogeneity at the center and at the boundary
of the coil when the size of the apparatus is increased. This
problem limits the scability of the process.
U.S. Pat. No. 5,435,881 presents an apparatus for generating a
suitably low pressure planar plasma. This apparatus comprises a
two-by-two or a larger array of alternating magnetic poles
(multipoles). The advantages cited in this patent are the
possibility to generate a large plasma by adding more varying
magnetic poles, therefore having very small area on non uniform
plasma.
However, such a design creates a dependency between the spacing of
the two-by-two magnetic poles and the excitation frequency as well
as the in-use operation pressure. This spacing depends on the mean
free path of the electrons which decreases when the pressure
increases. Accordingly, when a high operating pressure is necessary
for process requirements, the spacing between the two-by-two poles
must be drastically decreased. This becomes critical from a
technical point of view. The process also requires different
multipole distributions for different process pressures, which
decreases its flexibility and applicability to industrial
applications.
In all these prior art apparatus, there is a problem of gas
distribution uniformity in the chamber center. The gas distribution
is usually made using a ring located in the side wall of the plasma
chamber, which results in a lack of gas distribution uniformity at
the chamber center. This non-uniformity is even more acute when the
plasma chamber dimension increases. Moreover the gas distribution
means are usually made of metallic material, which perturbs the
magnetic field inside the chamber, and thus the plasma density.
Document EP-776 645 apparently discloses a plasma reactor or plasma
chamber in which a uniform gas distribution is achieved across a
wafer surface by injecting gas through a center gas feed silicon or
semiconductor ceiling.
This device is schematically illustrated on FIG. 1, and comprises a
plasma chamber 2, covered by a semiconductor ceiling 6 through
which gas injection tubes 12, 14 are drilled. Tube 14 in turn is
connected to a center gas feed pipe 16.
An overhead inductive coil antenna 4 is held in an insulating
antenna holder 8 connected to a plasma source power generator
through an impedance match circuit 10.
In this device, a voltage of about 2000 to 3000 volts is usually
applied to the coil antenna. A correspondingly very high electric
field can thus be induced in the dielectric window constituted by
the semiconductor ceiling 6. Such a capacitive coupling is very
detrimental.
This document further suggests choosing either a dielectric or
semiconductor, as a material for the top ceiling. However,
dielectric or semiconductor material results in a plasma being
created in tubes 12, 14, because of this capacitive coupling, which
is gas consuming and can damage the semiconductor ceiling.
SUMMARY OF THE INVENTION
The invention concerns an apparatus for generating a time-varying
magnetic field in a plasma processing chamber to create or sustain
a plasma within the chamber by inductive coupling, characterised in
that it comprises: a magnetic core presenting a pole face structure
or a unipolar pole face structure an inductor means associated with
the magnetic core, for generating a substantially uniformly
distributed time-varying magnetic field throughout the pole face or
unipolar pole face structure, means for injecting gas into said
chamber and through said magnetic core.
Since the means for injecting gas into the plasma chamber are
located or inserted through said magnetic core, a uniform or
controlled gas distribution is achieved in a plasma processing
chamber having such an apparatus for generating a time-varying
magnetic field, without any perturbation of the magnetic field.
Furthermore, the magnetic core electrostatically isolates the means
for gas injection from the inductor means. In other words, the
magnetic core plays the role of an electrostatic screen between the
means for gas injection and the inductor means, thus eliminating
the risk of capacitive coupling. The risk of plasma induction in
the gas injecting means themselves is reduced.
According to one embodiment of the invention, said means for
injecting gas into said chamber form a showerhead-like gas
injection.
For example, they advantageously comprise a plurality of injection
pipes distributed through the magnetic core. These injection pipes
are made of stainless steel material, or of an insulating
material.
An advantage of this embodiment is that the number of injection
pipes can be adapted without perturbing the magnetic field. In
other words, the number of pipes does not influence the magnetic
field inside the plasma chamber.
The diameter of the pipes can also be varied in a same magnetic
core. More gas is injected through larger pipes, than through
comparatively smaller pipes. It is thus possible to achieve a
controlled gas injection in the plasma chamber.
The injection pipes are connected to gas distributing means for
distributing gas to the injection pipes.
These gas distributing means are preferentially located on the side
of the magnetic core opposite to an inner space of said plasma
processing chamber
In one embodiment, they comprise a common gas injection pipe,
through which gas is distributed to the injection pipes. This
common gas injection pipe is preferentially made of stainless
steel, in particular in case of corrosive gases.
In another embodiment, the gas distributing means comprise a cover,
located on the side of the magnetic core opposite to the inner
space of the plasma processing chamber with a gap between said
cover and said magnetic core, said injection pipes emerging in said
gap.
A gas, or gases, is/are mixed in the gap between the cover and the
magnetic core, thus increasing the homogeneity of the gas
distributed or injected in the inner space of the plasma chamber.
The gap thus forms a gas distribution area above the magnetic
core.
Moreover, this arrangement avoids the connection of any gas
distribution pipe (the above mentioned stainless steel common gas
injection pipe) to the magnetic pole.
Preferably, the unipolar face structure is constituted by a single
pole face of unitary construction. In this way, the plasma
processing chamber is confronted with a substantially continuous
surface, which further contributes to enhance uniformity.
It is nevertheless conceivable to divide the pole face structure
into two or more pole faces or unipolar pole faces that confront
respective portions of the plasma processing chamber. This
alternative solution may be considered if the area to be covered by
the magnetic core is particularly large. The pole faces may then be
associated to respective inductors and power supplies whilst being
kept in phase to ensure that all the pole faces have the same
polarity at any one time. The pole faces may alternatively
physically depend from a common magnetic core and inductor.
In a preferred construction, the pole face structure constitutes an
end face of the magnetic core.
Advantageously, the magnetic core comprises at least one electrical
discontinuity in a path along a plane parallel to the pole face so
as to prevent the circulation of eddy currents around the core.
Indeed, the magnetic flux lines passing through the magnetic core
tend to create eddy currents that circulate in the plane of the
pole face, by Lenz's law. If these currents were free to circulate
around the core, they would create magnetic flux lines that oppose
those generated by the coil, with the effect of diminishing the net
magnetic field energy emitted from the pole face, and of creating
undesirable heating of the core.
The discontinuity can be in the form of one or more laminations.
The lamination(s) preferably extend radially from a point proximal
to or at the centre of the core to the to the periphery thereof.
The laminations may occupy the entire depth of the magnetic core,
as measured in the direction perpendicular to the pole face
structure.
The above problem of eddy currents is more pronounced in some core
designs than in others depending, for instance, on the core
material used, and on the operation frequency, and it may not
always be necessary to provide such a discontinuity.
The inductor means typically comprises a conductor arranged to form
one or more turns around at least a portion of the magnetic core.
It may be wound around the periphery of the magnetic core. The
inductor means may also comprise a planar winding recessed within a
groove pattern formed in the magnetic core, e.g. at the pole face
surface.
The inductor means is driven by a power supply preferably
delivering current at a frequency of around 10 kHz to 100 MHz, a
typical operating frequency being 13.56 MHz. A circuit for
impedance matching and phase factor correction can be provided
between the power supply and the inductor if required.
The invention also concerns a plasma processing apparatus
comprising: a plasma processing chamber having at least one field
admission opening or window at least one magnetic field generating
apparatus as defined above, arranged to create a time-varying
magnetic field in the chamber, power source means for driving the
magnetic field generating apparatus.
A barrier can be formed between a field emission surface and the
plasma environment in order to prevent that surface from
contaminating the chamber.
Such a barrier comprises a sheet of dielectric material maintained
between said pole face structure and an inner space of said plasma
processing chamber.
Alternatively, the barrier comprises at least one field admission
window between an inner space of said plasma chamber and said
magnetic field generating apparatus. In this case, the means for
injecting gas into the chamber and through said magnetic core
traverse the window.
In this case, said magnetic core presents a unipolar face adapted
to be applied against or in proximity to the window.
The magnetic core can easily be matched to the shape and dimensions
of an opening or of a window of the plasma chamber; it can present
e.g. a circular, rectangular or polygonal pole face as
required.
A window of the processing chamber need not necessarily be flat,
but may be curved, e.g. to follow the contour of a wall portion
from which it/they depend(s). The magnetic core can likewise
present a non planar pole face structure configured to follow the
curvature of the window(s) to provide uniform conditions inside the
chamber.
In the case of injection pipes, each of said injection pipes
traverses said window through a corresponding hole in said window,
and an end of each of said injection pipes is welded to the
periphery of said corresponding hole.
The plasma processing chamber may comprise several field-admission
windows. For example, it can be provided with two oppositely-facing
windows. If the chamber has a shallow configuration (circular or
square cross-section), the windows may be provided at each end of
the shallow walls, for example. If the chamber has an elongate
configuration (circular or square cross-section) the windows may be
formed on the elongate walls, e.g. disposed in one or several
pair(s) of oppositely-facing windows.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention and its advantages will be better understood from the
following description, given as non-limiting examples, of preferred
embodiments with reference to the appended drawings, in which:
FIG. 1 is a schematic view of a plasma chamber according to the
prior art,
FIGS. 2A, 2B and 2C are detailed views of a magnetic core according
to a first embodiment of the invention,
FIGS. 3A to 3C are schematic views of other time-varying magnetic
field generators which can be used in a plasma generating chamber
of the invention,
FIG. 4 is a detailed view of the plasma processing apparatus shown
in FIG. 2A,
FIG. 5 is a schematic cross-sectional view of a plasma processing
apparatus according to another embodiment of the invention,
FIG. 6 is a schematic cross-sectional view of a plasma processing
apparatus according to a further embodiment of the invention,
FIG. 7 is a schematic cross-sectional view of a plasma processing
apparatus according to a further embodiment of the invention, with
a cover and a gap for gas distribution,
FIGS. 8 and 9 are cross-sectional views of another embodiment of
the invention, with windows sealing the plasma chamber,
FIGS. 10A and 10B are a schematic general view and a detailed view
of a plasma processing apparatus according to another embodiment of
the invention,
FIG. 11 is a detailed view of a variant of the last embodiment of
the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
A first embodiment of the invention is illustrated on FIG. 2A,
where the processing chamber 20 is in the form of a shallow
cylindrical vessel in which a plasma is to be generated or
sustained. In common with classical processing chambers, it
comprises a support 24 for a workpiece 26, and at least one gas
outlet port 30 for connection to a pumping device (not shown) to
regulate the gas pressure inside the chamber.
The processing chamber 20 also comprises means for heating the
workpiece 26 via the workpiece support 24. To this end, the latter
is equipped with a heating resistance adapted to be in thermal
contact with the workpiece 26 and powered by a controllable heating
current source 32. The heating current source 32 operates in
conjunction with a temperature sensor (not shown) responsive to the
temperature of the workpiece to produce a constant set temperature
or a predetermined time-dependent temperature variation according
to requirements. Cooling means, not shown in FIG. 2A, can be used
to cool working substrate 24. For example, a cooling fluid
circulates through a fluid circulation conduit embedded in
substrate 24 and connected to a pump and a cooler.
The processing chamber 20 also comprises means for biasing the
workpiece 26, for example one or a number of electrical contacts
(not shown) at the level of the workpiece support 26 which connect
with workpiece either through cable connections or by direct
physical contact. The contacts are supplied by a bias source 34
outside the chamber 20 which can be set to provide an ac bias
(including radio frequencies), a dc bias or a ground bias.
The apparatus further comprises an inductive field energy field
source 38 as a time-varying magnetic field generator. The magnetic
field is created by a magnetic core 38 in association with an
inductor winding 40.
The magnetic core has a pole face 38a which faces the inner space
50 of the plasma chamber. Inductor winding 40 can be constructed
according to different variants, one of which is illustrated on
FIGS. 2A-2C; others will be explained in relation to FIG.
3A-3C.
The magnetic core 38 is connected to a core bias source 60.
The core 38 can be biased to produce a predetermined potential at
the level of the pole face 38a by means of a separate bias source
61 connected thereto. The bias source can be set to provide an ac
bias (including radio frequencies), a dc bias or to ground the core
38.
The combination of a magnetic core with the inductor serves to
increase and homogenize the magnetic field produced by the
inductor, the magnetic flux lines being uniformly distributed over
the pole face structure. This effect is particularly pronounced
given that a typical core material that can be used (like soft
iron, or an iron alloy or a ferrogmagnetic material) possesses a
very high permeability (.mu.) e.g. in the region of 1000 or
more.
The combination of the magnetic core and pole face structure
reduces the magnetic field "dead area" at the center of the
inductor, compared to magnetic field energy sources based on just
an inductor having a spiral path formed parallel to the plane of
the chamber opening 21.
As a result, it is possible to employ plasma processing chambers
having large opening areas and thereby to process correspondingly
large workpieces under homogeneous plasma conditions throughout the
active area. For instance, this type of apparatus can be used for
processing substrates of flat panel displays such as LCDs having
dimensions of around 0.5 m square or more.
Injection tubes or pipes 42, 44 traverse the magnetic core through
holes 39, 41 bored or drilled through said magnetic core as
illustrated on FIGS. 2B and 2C. As illustrated in FIG. 2B, the
tubes are preferentially perpendicular to pole face 38a or to a
plane defined by the magnetic core itself.
The injection tubes pass between the notches 46 in which coil or
winding 40 is inserted. Gas distributing means 48 for distributing
gas to the injection pipes are located on the side of the magnetic
core opposite to an inner space 50 of the plasma processing
chamber. In the illustrated embodiment, said gas distributing means
comprise common gas injection pipes 48, 51 through which gas is
distributed to the various injection pipes 42, 44. Pipe 51 is in
turn connected to gas feeding means 45, including gas containers,
pumping means, and their connecting means to pipe 51.
Injection pipes 42, 44 are made of stainless steel or of an
insulating material (for example: ceramic alumina). Pipes 48, 51
are made of stainless steel.
When gas is injected through pipes 51, 48, 44 and 42, it is sprayed
in gas jets 52, 54 into the inner space 50, thus forming a
showerhead-like gas injection. This results in an homogenous gas
atmosphere inside this inner space and in particular over workpiece
26.
In FIGS. 2A and 2B, pipes 42, 44 are schematically represented as
having the same diameter. However, they can also have different
diameters through a same magnetic core, facilitating the gas flow
control through this core. More gas is injected in regions where
pipes have a larger diameter than in regions where they have a
comparatively smaller diameter.
The magnetic core 38 can be made of any ferromagnetic material that
can be engineered to the required structural specification or of a
magnetic ceramic such as ferrite.
Where a relatively high field frequency is envisaged (e.g. 30 k Hz
to 5 MHz and more), the core can be made from a material composed
of a magnetic powder and dielectric binder such as sold under the
name of "Fluxtrol F" (RTM), from Fluxtrol Manufacturing, Inc. of
Troy, Mich., USA. or any other similar material. Such a material
has the advantage of providing excellent field uniformity in
combination with minimum eddy current losses, without recourse to
using a laminated structure.
In the embodiment of FIG. 2A, the magnetic core 38--and hence its
pole face 38a--are actively cooled by a closed circuit
refrigerating system. The latter comprises a fluid circulation
conduit (not shown on FIGS. 2A and 2B) embedded in the core 38 and
connected via an outlet 65 and an inlet 63 to a pump 62 and a
cooler 64.
In the construction shown in FIG. 2B a groove pattern 46 is formed
in the magnetic core 38 to receive the inductor winding 40. In the
example, the grooves 46 are exposed on the pole face 38a that
confronts the inner space of the processing chamber 20 and are
present substantially throughout that face. The pattern can form a
spiral or concentric closed path following a contour of the
magnetic core. The inductor winding 40 is arranged to be completely
recessed in the grooves 46, these being sufficiently deep to
accommodate one or more stacked winding layers. The inductor 40 has
for example a circular or a square cross-section.
Protrusions 39 situated between adjacent or neighbouring notches
46-1 and 46-2 are larger than the diameter of an injection tube 42
passing therethrough. Thus, these protrusions form an electrostatic
shield between tube 42 and winding 40, eliminating any coupling
between tube and winding.
FIG. 2C is a bottom view of the magnetic core 38, with grooves 46
forming a spiral path and holes 39, 41 all bored or drilled in or
through the magnetic core 38.
According to a variant shown on FIG. 3A, inductor 40 comprises a
metal tube wound as a coil having one or a number of turns
(typically three to ten) of equal radii, concentric with the core
38 and close to the periphery of the latter. The tube can e.g. be
made of copper or silver-plated copper and typically has a
cross-section of around 5 to 25 mm, possibly more. In the example,
the inductor winding is recessed within a groove 47 in the material
of the magnetic core 38.
This variant offers the following further advantage. If the core is
made from a material susceptible of eddy current losses, the latter
can be eliminated when relatively low frequencies are used by
employing the laminated core structure of FIG. 3A. Laminations 37
of insulating material divide the core 38 into electrically
isolating segments radiating from a central portion so as to
prevent the circulation of eddy currents. Alternatively, the
segments 38c can be separated by an air gap.
In the variant of FIG. 3A and 3B fluid circulation conduit 65 of
the refrigerating system can comprise a few turns of piping around
the magnetic core. For improved heat dissipation, the piping can be
associated with fins or equivalent structures embedded in the
core.
FIG. 3B is a cross-sectional view of the structure of FIG. 3A. It
clearly shows the gas injection pipes 42, 44, 48, 51, pipes 42 and
44 traversing the magnetic core 38. The last one plays here also
the role of electrostatic screen between pipes 42, 44 and inductor
means or winding 40, eliminating any coupling between said pipes
and said winding.
FIG. 3C is a cross-sectional view of another variant of magnetic
core structure which can be used according to the invention. The
conductor winding 40 is formed around the periphery of the magnetic
core 38. In this example, the conductor has a square section and
forms two winding layers. This figure also clearly shows gas
injection pipes 42, 44, 48, pipes 42 and 44 traversing the magnetic
core 38, the electrostatic screen between pipes 42, 44 and inductor
means or winding 40. This screen eliminates, as in the other
embodiments and variants explained above, any electrostatic
coupling between said pipes and said winding.
In any of the above embodiments and variants, the number of turns
forming the inductor is determined, inter alia, by the impedance
matching with the power source 61.
The power source 61 is of a classical design, comprising a
radio-frequency (RF) generator whose power output is connected to
the coil 40 via a tuned circuit (not shown) having a capacitive
element for impedance and phase factor matching to the load.
Typically the generator 61 operates at a frequency of 13.56 MHz,
but this value can be e.g. from a few tens of kHz to several tens
of MHz depending on the specifics of the design.
The current from the high-frequency power source 61 circulates
around the coil 40 and generates a magnetic field whose flux lines
are substantially perpendicular to the plane of the coil, at the
region within the coil, and hence perpendicular to surface 38a. The
flux lines alternate at each cycle of the high-frequency current
flowing in the coil and create a magnetization of the core, and
hence perpendicular to surface 38a. The flux lines alternate at
each cycle of the high-frequency current flowing in the coil and
create a magnetization of the core 38 with a polarity that likewise
alternates at each cycle. The unipolar pole face 38a of the
magnetic core is thus magnetized in alternation between north and
south polarities but, at any one moment, possesses the same
polarity throughout its area, and is in this respect considered as
a unipolar pole face. The high permeability of the core material
ensures that the magnetic field lines from the unipolar pole face
38a are of uniform density. The space 50 inside the plasma
processing chamber 20,--and hence the workpiece 26,--experiences a
correspondingly uniform plasma environment.
In the variants of FIGS. 2B and 3C, the magnetic core 38 can
present a break in the electrical path for eliminating eddy
currents, or no such break.
Also, the core cooling system in these variants comprises a cooling
plate 53 placed in thermal contact with the top surface of the core
38 and inductor winding 40 (i.e. the surface opposite the pole face
38a). The cooling plate 53 comprises a conduit connected to a
cooling system as described in FIG. 2A and can be traversed by
injection pipes 42, 44.
This cooling plate can alternatively--or additionally--comprise a
heat-sink structure adapted to radiate heat. The heat-sink
structure can in this case be associated with a force-air flow.
Also, in any of the above embodiments and their variants, the
inductor 40 can have a cross-section other than square, e.g.
circular. Furthermore, the geometry of the plasma processing
chamber 20,--and hence the magnetic core,--is cylindrical. However,
the same concepts can be readily transposed to other geometries
(square, oblong, oval or polygonal) by simple adaptation.
The field energy source also forms a sealed cover with respect to
the inner space 50 of the plasma chamber. Sealing means are
disposed between the periphery of the plasma chamber and the
magnetic core.
In the above illustrated embodiment and its variants, the periphery
of the magnetic core 38 defines a shoulder portion 70 that rests on
a corresponding rim portion 72 around the opening of the process
chamber via a sealing gasket 74.
Respective flanges 76a, 76b project outwardly from the shoulder 70
and the rim portion 72 to hold and tighten the magnetic core 38
against the process chamber 20 by nut-and-bolt fasteners 78 to
ensure a proper seal by the gasket 74. The magnetic core 38 is
electrically isolated from the mechanical structure forming the
chamber 20 so that it can be biased by the bias source 61
independently of the chamber. In the example, the electrical
isolation is effected by the sealing gasket 74. More generally, the
sealing means mentioned above are also used as means for
electrically isolating the magnetic core form the plasma
chamber.
A dielectric material sheet 80 e.g. of quartz, glass such as Pyrex
(RTM) a ceramic or polymer can be provided between the pole face
38a and the space inside the chamber 20 to prevent possible
contamination of the plasma gas by the pole face material. In the
example of FIG. 2A, the sheet 80 is applied against the pole face
38a and held by the latter, e.g. by adapted mounting brackets.
Alternatively, the sheet of dielectric material 80 may be
maintained without contacting the pole face 38a, e.g. by means of a
peripheral mounting recess 82 formed at the shoulder portion 70 of
the magnetic core 38, as shown in FIG. 4.
In this case, means may be provided to equalize the pressures
respectively at the space between the outer face of the sheet 80
and the pole face 38a and at the space between the inner surface of
the sheet and the inner walls of the chamber 20. Such means can be
in the form of a simple opening or group of opening, or a valve
arrangement, e.g. at an edge of the sheet.
If a valve is used, means may be provided to control the latter
such that a pressure equalization can take place whilst the chamber
is being prepared e.g. during gas exhaustion and establishing the
process gas conditions, but closed when a plasma process is being
performed so as to prevent any contaminant from the energy field
source reaching the process gas. conditions, but closed when a
plasma process is being performed, so as to prevent any contaminant
from the energy field source reaching the process gas.
The dielectric sheet 80 experiences the same pressure on both of
its sides and needs not therefore be rigid to the extent required
for a window that has to withstand atmospheric pressure. In this
case, the force of atmospheric pressure is supported by the
magnetic core 38, which is normally sufficiently rigid for that
purpose. If needs be, the core can be strengthened to ensure that
it does not distort significantly when submitted to a pressure
differential of one atmosphere.
Depending on operating conditions, it may be necessary to take
appropriate measures to avoid a plasma being formed in the space
between the dielectric sheet 80 and the pole face 38a. One solution
is to ensure that the gap between the dielectric sheet and the pole
face is kept as small as possible, e.g. less than 1 mm, possibly
less than 0.5 mm.
Holes are made in sheet 80 to let tubes or pipes 42, 44 traverse or
go through, so that they can inject gas into inner space 50. The
end of tubes 42, 44 are welded to sheet 80.
FIG. 5 illustrates a further embodiment where the workpiece 26 is
held suspended by a support structure 84. The workpiece 26 is
heated by an infrared heating device 86 beneath the workpiece and
connected to an infrared heating power source 98.
Substrate is biased with a substrate bias source 92.
Other reference numbers designate the same features as on FIG.
2A.
In the embodiments described above, the plasma chamber has one
energy field admission opening.
FIG. 6 is a partial plan view of another embodiment which is
analogous to the above embodiments, but where the process chamber
has more than one (two in the illustrated example) energy field
admission openings.
Each opening is disposed so as to allow exposure of different
portions of a workpiece 26 to the plasma generating or enhancing
effect of the energy field.
In the example of FIG. 6, the plasma processing chamber 20 has the
basic configuration shown in FIG. 2A.
Two openings 94a and 94b are provided, one at each respective end
face of the chamber 20, each opening 94a, 94b being associated with
an inductive energy source for creating a plasma condition inside
the chamber. In the example, the inductive energy source is a
time-varying magnetic field generator as in the previous
embodiments. Each inductive energy source is traversed by
corresponding tube or pipe 42, 44, 43, 45 for gas injection. Gas
distributing means 48, 49 for distributing gas to the injection
pipes are located on the side of each magnetic core opposite to an
inner space 50 of the plasma processing chamber. In the illustrated
embodiment, said gas distributing means comprise a common gas
injection pipe 48, 49 through which gas is distributed to the
various injection pipes 42, 44, 43, 45.
The openings 94a, 94b, time-varying magnetic field generators 38,
39 and mutual disposition between the opening and the generator,
core biasing means 60a, 60b and core cooling means 62a, 62b, 64a,
64b, are in every respect identical to what has been described in
respect of the first embodiment and its variants, and shall
therefore not be repeated for conciseness. It can be noted that
while the illustrated example provides separate core biasing means
60a, 60b for each time-varying magnetic field generator and
separate cooling systems 62a, b, 64a, b, other arrangements can be
envisaged.
Also, the magnetic core variants illustrated on FIGS. 3A, 3B and 3C
are applicable to this embodiment.
The workpiece 26 has upper and lower faces that occupy virtually
the entire projected area of the respective openings 94a, 94b . It
is held suspended by a support structure 84, mid-way between the
two windows, such as to allow each of the upper and lower surfaces
to be exposed directly to its respective opening. In this way, it
is possible to treat both faces of the workpiece 26 simultaneously
and under the same optimal conditions with regard to plasma energy
generating field induced from the opening. It is also possible to
process one face of two workpieces placed back-to-back.
The support structure 84 is designed to produce no shadowing of the
field energy from either of the two opening 94a, 94b. In the
example, the support structure 84 depends from inner wall portions
of the chamber 20, mid-way between the two end faces. The innermost
part of the support structure 84 is equipped with an edge grip or
edge rest 85 for the workpiece 26.
In order to ensure an improved homogenous gas flow conditions at
each exposed face of the workpiece, separate gas outlets can be
provided respectively at the upper and lower portions of the
processing chamber 20.
The upper and lower portions can be open to communicate with each
other to allow a uniform mixing of gases.
Alternatively, they can be separated by a sealed partition adapted
to surround around the workpiece 26 in a gas-tight manner so that
separate gas conditions can be established on respective faces of
the workpiece 26. To this end, the workpiece support structure 84
can form a part of the partition in conjunction with the workpiece
26. Edge grips or edge rests 85 can in this case be made to
surround the entire periphery of the workpiece 26 and be provided
with a gas tight seal at the interface with the edge of the
workpiece. The support structure 84 is likewise sealed around the
entire periphery of the internal walls of the chamber 20.
As in the first embodiment, means are provided for heating and
biasing the workpiece at the level of the support structure 84. In
this case, however, heating of the workpiece 26 is effected by
means of heating lamps 101, 101a disposed at corners of the chamber
20 so as not to obstruct the field of view from the openings 94a,
94b or otherwise cause shadowing of the energy field. The lamps
101, 101a have a transmission optics or reflector to produce a
uniform distribution of heat onto the workpiece 26. Both faces of
the workpiece 26 can be heated simultaneously. The electrical
connections to the lamps 101 are not shown in the figure.
The workpiece biasing means comprise one or a set of electrical
contacts provided on the support structure 84 so as to interface
with the workpiece, e.g. at the level of the edge grips 85. The
contact(s) are connected to a bias source 102 that can produce
either an ac bias (include radio frequencies), a dc bias or a
ground bias.
The above-described arrangement of the workpiece heating and
biasing means does not interfere with the passage of the energy
field to the faces of the workpiece from the respective opposite
openings 94a, 94b.
The respective inductors of the time-varying magnetic field
generators 38, 39 can be connected in parallel to a common power
source 61 (as shown in FIG. 6) or in series, with an impedance and
phase factor matching circuit adapted as required. Alternatively,
they may each be connected to a separate power source.
In each side of the chamber 20 a dielectric material sheet 80a, 80b
can be provided between the corresponding pole face 38a, 39a and
the inner space of the chamber. Such a sheet is of the same
composition and has the same purpose as already described
above.
FIG. 7 is another embodiment of the invention. The magnetic core
and the plasma chamber are identical to those of the first
embodiments and its variants. In addition it comprises a cover 91
situated above the magnetic core 38. The bottom surface of the
cover is situated at a certain distance from the upper or top
surface of the magnetic core, thus defining a gap 93 there between.
Holes 95 are bored or drilled through cover 91, which can be made
of stainless steel or aluminium or any insulating material. It can
be made of the same material as pipes 42, 44 or as pipes 48, 51
(FIG. 2B), which facilitates welding of said pipes with cover
91.
Injection pipes 42, 44 are provided through the magnetic core 38 as
already described above. Each of these injection pipes has one end
opening to the inner space 50 and its other end opening to gap 93.
Like in the first embodiment, gas distributing means for
distributing gas to the injection pipes 42, 44 are located on the
side of the magnetic core 38 opposite to the inner space 50 of the
plasma processing chamber. However, in the embodiment of FIG. 7,
the gas distributing means are formed of, or comprise the gap 93
and the holes 95. Gas is first injected in the gap 93 through holes
95. Injected gas is mixed in gap or mixing chamber 93 and is then
injected towards the inner space 50 of plasma chamber 20 through
pipes 42, 44.
In this embodiment, gas injection is performed roughly in two
steps. In a first step, gas is injected into gap 93 and is mixed
therein. It is also equally distributed over the various open ends
of pipes 42, 44. In a second step, mixed gas is injected to inner
space 50 through pipes 42, 44. Actually part of the gas is injected
into pipes 42, 44 while the rest of the gas is still in gap 93.
The structure of plasma gas chamber of FIG. 7, and in particular
the two-step gas injection, enhances gas mixing which is
particularly advantageous when using gas mixtures. It also enhances
gas homogeneity since a first homogenisation occurs in gap 93.
The embodiment of FIG. 7 is compatible with the structure of FIG.
6, two covers with a gap between each of them and the corresponding
magnetic core replacing distribution pipes 48, 51, with the same
advantages as explained above in relation to FIG. 6.
FIG. 8 illustrates another embodiment of the invention. Reference
numbers identical to those of FIG. 2A designate elements or
features which are the same or correspond to those of FIG. 2A. In
addition, a top face of the chamber is provided with a window 122
which is made of quartz or other dielectric material such as to
allow an energy field to enter inside the chamber by inductive
coupling and thereby create or sustain the required plasma
processing conditions. The window 122 is maintained on a rim
portion 124 of the chamber 20 through a gas-tight seal. The
rigidity of the window 122 and quality of the seal must be such as
to withstand the collapsing force of atmospheric pressure when low
pressure gas or partial vacuum conditions exist inside the
chamber.
Window 122 forms a barrier between inner space 50 and surface 38a,
preventing the last one from contaminating the chamber.
The size of the window 122 determines the area over which the
plasma conditions are generated or sustained inside the chamber 20,
and consequently the area of the workpiece 26 that can be processed
under optimum conditions. In the example, the window 122 occupies
almost the entire cross-section of the chamber, enabling the
workpiece 26 to occupy a correspondingly large area.
The field energy generator 38 induces a time-varying magnetic field
inside the chamber 20 through the window 122. It is provided
outside the chamber 20 and against the window, slightly spaced from
the latter.
The magnetic field is created by a magnetic core 38 in association
with an inductor winding 40, having a structure as illustrated for
example on FIGS. 2B, 2C, 3A, 3B or 3C. Winding 40 circulates a
current from a high-frequency electrical power source 61.
The magnetic core 38 is connected to a core bias source 60.
The magnetic core 38 presents a face 38a having substantially the
same size and shape as the window 122 and positioned in alignment
with the latter. To ensure minimum energy loss, the distance
between the unipolar pole face 38a and the window 122 is kept small
(a few mm) or even zero.
The inductive energy source is traversed by tubes or pipes 42, 44
for gas injection. Gas distributing means 48 for distributing gas
to the injection pipes are located on the side of each magnetic
core opposite to an inner space 50 of the plasma processing
chamber. As in the above embodiments, the magnetic core of the
inductive energy source forms an electrostatic screen between pipes
42, 44 and inductor means or winding 40. This screen eliminates, as
in the other embodiments and variants explained above, any coupling
between said pipes and said winding.
FIG. 9 is a partial plan view of another embodiment, where the
process chamber has more than one window, for example two windows,
for admitting field energy, in conformity with another aspect of
the present invention.
Each window is disposed so as to allow exposure of different
portions of a workpiece 26 to the plasma generating or enhancing
effect of the energy field.
In the example of FIG. 9, the plasma processing chamber 20 has the
basic configuration shown in FIG. 8, except for the two windows
122a, 122b provided, one at each respective end face of the chamber
20.
To each window 122a, 122b is associated an inductive energy source
for creating a plasma condition inside the chamber. The inductive
energy source is a time-varying magnetic field generator as in the
previous embodiments, for example as illustrated on any pf FIGS.
2B, 2C, 3A, 3B or 3C. Each inductive energy source is traversed by
corresponding tubes or pipes 42, 44, 43, 45 for gas injection. Gas
distributing means 48a, 48b for distributing gas to the injection
pipes are located on the side of each magnetic core opposite to an
inner space 50 of the plasma processing chamber
The workpiece 26 is connected to the workpiece bias source 72.
In both variants of FIGS. 8 and 9, the injection pipes traverses
holes arranged in window 122, 122a, 122b and the periphery of one
end of each pipe is welded to the periphery of the corresponding
hole in window 122, 122a, or 122b.
Both embodiments of FIGS. 8 and 9 are represented with gas
injection means formed of gas injection pipes 48a, 48b. However,
gas distribution means can instead comprise cover means situated on
each outer side of magnetic core 38 and 38a, forming a gap with
said core, as explained above in relation with FIG. 7. Such gas
distribution means have the advantages already disclosed above,
namely improved mixing and homogeneity of the injected gas.
For the rest this embodiment is identical to what was described
above in relation with FIGS. 6 and 8.
FIG. 10A shows a third embodiment of the invention adapted to a
plasma processing chamber 20 having a cylindrical shape in which
the field energy is delivered through the side wall 20a of the
chamber. In the example, two field-admission windows 122a, 122b are
formed at corresponding openings in the side wall 20a at
diametrically opposite positions. The windows 122a, 122b are made
of dielectric material such as quartz and provide a pressure-tight
seal for the openings. Each window gives direct access to a
different surface portion of a workpiece which, in the example, is
held inside the chamber by means of a stage 142 arranged to produce
no shadowing effect for the energy field from each of the two
windows.
The field energy is provided by a time-varying magnetic generating
apparatus 138a, 138b according to the first embodiment of FIG. 2B
or 2C or its variants illustrated on FIGS. 3A-3C, each apparatus
being associated to a corresponding window 122a, 122b. However, the
magnetic pole pieces are in this case rectangular cylindrical
segments with the pole face 138a confronting the window curved
concentrically with the principal axis of the cylindrical wall of
the plasma chamber. The pole pieces 138 may be flush against their
respective window or at a small distance from the latter (FIG.
10B). The weight of the pole pieces 138 is supported by a mounting
structure 141 separate from plasma processing chamber 20.
As shown in FIG. 10A, each core 138 is cooled by independent
cooling means 162, 164 based on the embodiment of FIG. 2A.
Likewise, each core 138 is biased independently.
The workpiece 26 is biased by one or a set of contacts (not shown)
on the stage 142 connected to a workpiece bias source 172 providing
the same functions as in the above-described embodiments.
Heating of the workpiece 26 is effected by a bank of infrared lamps
101 mounted on the stage 142 and connected to a heating power
source 198 to form a classical infrared heater. Additional infrared
heating lamps can be provided inside the chamber 20 at locations
where they do not obstruct the energy field reaching the workpiece
26 from the different windows 122a, 122b.
Although the figure shows the chamber to have two energy field
admission windows 122a, 122b, it is clear that more windows can be
provided in the same manner if required. For instance, the chamber
20 can be provided with four, equally spaced windows e.g. for
processing four faces at right angles of a workpiece or one face of
four workpieces.
According to the invention, gas injection pipes traverse magnetic
cores 138a, 138b. These pipes 142, 144 are not represented on FIG.
10A but are shown on FIG. 10B. They have the same purpose as in the
other embodiments and are separated from the winding, which are
used in combination with core 138 to create the magnetic field
inside plasma chamber 20, by the electrostatic screen formed by the
core itself.
FIG. 11 is a partial plan view of another embodiment in which the
plasma processing apparatus of FIG. 10A is modified by having the
openings closed off and sealed by the field energy source, as in
the embodiments of FIGS. 2A or 5 or 7.
In the figure, the magnetic core 138 has a peripheral shoulder
portion 150 that presents a contact face adapted to fit against the
portion of the chamber wall 20a around the opening via a gasket 154
to offer a gas-tight seal. The magnetic core 138 and gasket 154 are
fixed onto the chamber wall by a peripheral mount 164. The weight
of the magnetic core 138 is additionally supported by the
independent support structures 141 shown in FIG. 10A.
In the example, a dielectric sheet 180 is conformed to the
curvature of the pole face 138a and is supported by the latter. It
may alternatively be maintained spaced from the pole face e.g. by a
peripheral recess similar to the one shown in FIG. 4. This
dielectric sheet has the same purpose as sheet 80 on FIGS. 2A and
4, 5, or 6.
The embodiments of FIGS. 10A, B or 11 can also use a gas
distribution system as disclosed above in relation with FIG. 7. In
this case, a cover is situated on the outer side of each magnetic
core 138a, 138b, said cover forming a gap with core 138a, 138b for
gas mixing and homogenisation before injection into plasma
chamber.
The cores 138a, 138b are connected to core bias sources 174b, 174c,
respectively.
In all the above embodiments, the magnetic core and the winding
extend over a surface which is approximately as large as the whole
plasma chamber itself, with the advantage of allowing treatment and
processing of large surfaces.
The invention applies as well to plasma chambers where the magnetic
core and the winding are not as large as the plasma chamber itself.
The plasma chamber then has the same characteristics as illustrated
on any of FIGS. 2A-11, but with a winding not extending on the
whole surface of the magnetic core.
The invention also concerns a plasma processing chamber as
disclosed above, the magnetic core or its unipolar pole face
structure having an active field emission area whose size and shape
is smaller than an area of the field admission opening or the field
admission window of the chamber.
In both cases, gas injection pipes still traverse the magnetic core
38. In the central portion of the core, the core forms an
electrostatic screen between the pipes and the winding, as already
explained above.
In all the embodiments described above, pipes 42, 43, 44, 45, 142
and 144, are schematically represented as having the same diameter.
They can also have different diameters for facilitating gas flow
control. More gas is injected in regions where pipes have a larger
diameter than in regions where they have a comparatively smaller
diameter.
The present invention, in any of its aspects, can be implemented in
a wide variety of applications such as: etching; plasma enhanced or
plasma assisted chemical vapour deposition (respectively PECVD or
PACVD); cleaning and surface preparation of workpieces;
passivation; and plasma ion implantation.
* * * * *